chore(python-library): use sphinx 1.5.5 for the docfx job

Originally tested at:
googleapis/python-texttospeech#89

This change will fix the missing docstring in the yaml files.

Source-Author: Takashi Matsuo <tmatsuo@google.com>
Source-Date: Thu Sep 10 04:12:14 2020 +0000
Source-Repo: googleapis/synthtool
Source-Sha: ffcee7952b74f647cbb3ef021d95422f10816fca
Source-Link: googleapis/synthtool@ffcee79

noxfile.py

@@ -171,7 +171,9 @@ def docfx(session):
     """Build the docfx yaml files for this library."""
 
     session.install("-e", ".")
-    session.install("sphinx<3.0.0", "alabaster", "recommonmark", "sphinx-docfx-yaml")
+    # sphinx-docfx-yaml supports up to sphinx version 1.5.5.
+    # https://github.com/docascode/sphinx-docfx-yaml/issues/97
+    session.install("sphinx==1.5.5", "alabaster", "recommonmark", "sphinx-docfx-yaml")
 
     shutil.rmtree(os.path.join("docs", "_build"), ignore_errors=True)
     session.run(

synth.metadata

@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "d302f93d7f47e2852e585ac35ab2d15585717ec0"
+        "sha": "ffcee7952b74f647cbb3ef021d95422f10816fca"
       }
     }
   ],